1. Field of the Invention
The present invention relates generally to a method and apparatus for video telephony in a portable terminal, and more particularly, to a method and apparatus for, when image frames are cumulatively stored during a video telephony operation of a portable terminal, selectively displaying the cumulatively-stored image frames to prevent a processing delay of the image frame.
2. Description of the Related Art
The International Mobile Telecommunications (IMT)-2000 system, used as the third-generation (3G) mobile communication system, provides a world-wide wireless telephony network and thus enables many users to perform worldwide wireless telephony via portable telephones. Wideband Code Division Multiple Access (CDMA) (WCDMA) mobile communication systems such as the IMT-2000 system and the Universal Mobile Telecommunications System (UMTS), are suitable for high-rate data transmission and thus provide not only a voice telephony service but also image services such as an Internet service and a video telephony service.
FIG. 1A illustrates an apparatus for processing image frames received in a conventional portable terminal and FIG. 1B illustrates a graph showing the time-dependent number of the received frames. FIG. 2A illustrates an apparatus for processing image frames cumulatively received in a conventional portable terminal and FIG. 2B illustrates a graph showing the time-dependent number of the cumulatively-received frames.
In general, as illustrated in FIG. 1A, after one image frame 107 is received in an RX frame buffer 101, a portable terminal decodes the received image frame 107 by a decoder 103 and displays the resulting image on a display unit 105 prior to receiving the next image frame. By doing so, as illustrated in FIG. 1B, the portable terminal processes the received image frame within the maximum frame decoding/displaying time on a one-by-one basis, thereby providing a real-time video telephony service.
However, received image data may be discarded due to a CRC(Cyclic Redundancy check) error and an RX data rate of a modem in the portable terminal, and received image frames may fail to be stored and processed in the portable terminal at the same frame rate as that of a counterpart terminal due to the real-time uplink/downlink operations of a Dual-Port RAM (DPRAM). Therefore, as illustrated in FIG. 2A, the received image frames may be cumulatively stored in an RX frame buffer 201.
In addition, although a high-speed processor must be used to process the received image data in real time most conventional portable terminals do not use the high-speed processor in order to reduce costs. Thus, the conventional portable terminal fails to properly decode and display the received image frame, causing problems such as frame process delay and cumulative delay. For example, when two or more received image frames 207 accumulate in the RX frame buffer 201 as illustrated in FIG. 2B, the decoder 203 and the display unit 205 must decode and display the two or more accumulated image frames 207 within the time for decoding/displaying one image frame, which causes a display time for each image frame to be too short. Moreover, the decoder 203 may fail to process even one image frame within the time for decoding/displaying one image frame and thus the received image frames may continue to accumulate in the RX frame buffer 201, causing a continuous frame processing delay.
As described above, the number of the received image frames varies according to circumstances and also the frame processing time in the decoder and the display unit varies according to CPU occupation circumstances. Consequently, a display delay occurs due to a continuous frame processing delay. In addition, the processing delay causes incorrect synchronization between voice data and image data.